Stencil printer



March 12, 1968 K. F. TRIPP 3,372,638

STENCIL PRINTER Filed May 22, 1967 1:55 FIGURE 2 VACUUM KEN/V5777 F 477m? @y; WM AWL 1 United States Patent 3,372,638 STENCIL PRINTER KennethF. Tripp, Hancock, N.H., assignor to Marlrern Machine Company, Keene,N.H., a corporation of New Hampshire Filed May 22, 1967, Ser. No.640,049 6 Claims. (Cl. 101-114) ABSTRACT OF THE DISCLOSURE Thisinvention relates to a stencil printing device in which a stencil membersurrounded by a flexible wall is brought into intimate contact with thesurface being decorated by creating a vacuum in the space between thestencil and the surface, and simultaneously utilizing atmosphericpressure to transfer an inked image through the stencil, to the surface.

This invention relates to improvements in printing and decorating with astencil, and more particularly relates to stencil printing anddecorating of non-rigid surfaces, as for example the plastic containerscurrently in vogue in the dairy field and other segments of the foodindustry.

As a general statement, the printing quality on such containers is nottoo rigorous. However, to achieve any measure of acceptable printing onthese surfaces does require intimate contact between the printing memberand the surface being decorated. Because such containers are massproduced through a chemical blowing process, they do not provide auniformly plane surface for such intimate contact to occur. In view ofthese limitations and requirements, coupled with the fact that from apractical point of view these containers must be printed at a fairlyhigh rate of speed, there are but few prior art techniques which lendthemselves to practical modes of decoration of such surfaces.

These prior art methods have been generally limited to conventionalscreen processes, thermographic transfers (e.g. heat labeling), orpasted paper labels. None of these, or other known techniques, isentirely satisfactory.

In conventional screen printing, a squeegee sliding across the stencilforces ink through it, making a print on the surface being decorated byadhesion on contact with the ink. There have been several prior artattempts to achieve similar results by employing pneumatic forces toextrude the ink through the stencil. Such pneumatic extrusion of the inkhas the disadvantage, however, that because the full area of the stencilmakes contact with the surface, there frequently are air pockets oftrapped air which, being unable to escape, prevent local intimatecontact, thereby preventing an image transfer at these pointsaccordingly resulting in an incomplete or mottled print. Additionally,the ink not transferred at these points remains as an excessaccumulation which will create smears during subsequent print transfers.

In the case of thermographic transfers and pasted paper labels, thereare storage and deterioration problems in addition to using complexequipment for registration and adhesive application to the surface beingdecorated.

To use any of these prior art decorating processes requires that thesurface being decorated be sufficiently nonyielding to resist the forcenecessary to transfer the decoration from the printing member to thesurface. Because the surfaces of many plastic containers are inherentlynon'rigid, and therefore yieldable, such containers are usuallypressurized with clean air (conforming to established standards,particularly in the food industry) in an attempt to render thesesurfaces more rigid during the printing operation. The need for thispressurization, coupled with the cleanliness requirements of the air areobvious drawbacks.

Further, because of the large space requirements which are necessary touse these prior art printing techniques, these containers can generallyonly be decorated on their vertical surfaces, which is often of littlevalue since the consumer who generally sees only the top of thecontainer when they are stored below eye level in a side-bysiderelationship cannot identify the product with ease.

This invention overcomes these above limitations by providing anapparatus and method of decorating a surface in which intimate contactbetween a printing stencil and the surface being decorated is achievedby employing vacuum techniques. More specifically this inventionprovides for the use of partial vacuum to bring a stencil member and thesurface to be decorated into intimate contact with one another.

It is accordingly among the various objects of this invention to providean apparatus and method for rapidly decorating rigid and non-rigidsurfaces with a stencil.

It is a further object of this invention to provide a stencil printingprocess and apparatus which permits such an image or decoration to beplaced on an exposed surface regardless of its attitude of orientation.

It is yet another object of this invention to provide an apparatus forstencil printing whose space requirements are only slightly larger thanthe total print area of the image to be transferred.

It is a still further object of this invention to provide an apparatusfor stencil printing whose physical design can be varied in size fromlarge to small with equal facility depending on the size of the desiredimage and whether the device is to be permanently installed or whollyportable.

These and other objects of this invention will become more apparent fromthe following description when taken in conjunction with theaccompanying drawings in which:

FIGURE 1 is a schematic vertical cross-sectional View of the apparatusof this invention; and

FIGURE 2 is a bottom view of the device shown in FIGURE 1.

Referring now to the drawings, shown in schematic cross-sectional viewin FIGURE 1 is printer 1t}, comprised of an open-ended, cylindricalhousing 1! carrying a tautly stretched stencil 12 across its lower end.Carried within this cylindrical housing, behind the stencil, is aquantity of viscous ink 13. Though the illustration depicts housing 11as being cylindrical in form, it is to be understood thatan open-endedhousing of any shape will suifice so long as it can carry a stencilattached to one end thereof. Carried on top of the mass of ink 13 is afollower 14 which is free to move with the ink level in the housing, itsfunction being more fully explained hereinafter.

Surrounding the lower periphery of housing 11 is an elastomeric flangedseal 15 with its flanged portion 16 in sealing engagement with the outerperiphery of the housing. The remaining portion of seal 15, isdimensioned so that its lower surface 15a extends somewhat beyond thesurface of stencil l2 and has its body portion 15b in spaced-apartrelation to the housing thereby forming an annular recess 17therearound. Exhaust port 13 connected to a conventional vacuum pump(not shown) communicates with recess 17 through seal 15.

In operation, when elastomeric surface 15a is brought into contact witha surface 22, which is to be printed, a vacuum is withdrawn throughexhaust port 18 so as to evacuate chamber 21, Le. that volume bounded byannulus l5, stencil 12 and surface 22.

The evacuation of chamber 21 forces stencil 12 and surface 22 together,simultaneously compressing seal 15 enough to permit this contact.Concurrently with this action, as the vacuum increases within chamber2%, atmospheric pressure acting on the surface of follower I4 istransmitted to ink mass 33 thereby forcing it through stencil 12 intointimate contact with surface 22. it is at this moment of intimatecontact that the desired image is formed on the surface. It should berecognized that where ink viscosity is high enough so that the ink doesnot readily flow, the absence of follower 14 would permit cavitationand/ or tunneling to occur within ink mass 13, eventually reaching thestencil, thereby rendering this device ineffective. Accordingly, as ink13 is Consumed, follower i4, riding on top of this ink as a piston, iscorrespondingly lowcred and simultaneously scrapes the ink from thewalls of housing 11 maintaining ink mass integrity.

The time necessary to cycle this apparatus for printing one image variesof course with such things, for example, as how rapidly the partialvacuum can be effected, how viscous the ink is, and the extent of sealdeformation necessary to bring the stencil into contact with the surfacebeing printed. In the illustrated embodiment the image cycle (i.e. thetime for bringing the stencil and surface together, time for intimatecontact therebetween and time for readmitting air to chamber 21) isapproximately /2 second; the sealing surface extends approximately 3.0mm. beyond the surface of stencil I2; and the ink has viscosity inexcess of 100,000 centipoises.

In bringing about the intimate contact necessary between stencil 12 andsurface 22 for a good image transfer, it is obvious that there will berelative motion taking place. This motion may comprise the surface 22alone moving toward the stencil; the stencil 12 alone moving toward thesurface 22; or both of these motions may act together in contributing tothe bringing about the requisite intimate contact.

Generally, in employing this invention, ink viscosities are limited inrange only to the extent that there be no spontaneous flow through thestencil, regardless of its attitude, i.e. whether face-up, or face-down,or some position in between. As to limitations of high ink viscosity,the ink must flow sufficiently to at least replace at the stencilsurface What the previous print has removed.

This invention additionally envisions embodiments of apparatus which aresubstantially larger, or substantially smaller than that described, thelatter having attributes of portability. In any of these comtemplatcdmodifications however, print surface area is of little concern to theperformance of this apparatus, since effective unit pressures areindependent of areas.

For illustration, this invention has been described in terms of printingon a plane surface. However, it should be noted that the decoratingcurvilinear and other nonplanar surfaces can easily be accomplished withthis device also, provided only that the stencil has sufiicient slack orlooseness to conform with the surface being decorated. The stencilconforms with the shape of such a non-planar surface on its first cycleof operation and thereafter retains the shape of this configurationbecause of the non-flowing characteristics of the high viscosity inkemployed. In this circumstance the ink serves somewhat as a structuralmember of the printing apparatus by maintaining the stencil in thedesired shape.

Though this disclosure describes the ink-containing housing 11, i.e.ink-package, as being rigid, it is obvious, in light of this disclosure,that such an ink-package can also be made of collapsible material, solong as that portion to which the stencil is connected remainssufficiently rigid to hold the stencil taut. In such a case if thecontainer end is closed, follower 14 would obviously not be needed.

Further, though the flanged seal 15 has been identified as beingeiastorneric in nature, it should be obvious, in light of the foregoingthat other equivalent structures and/ or materials may be suitable solong as they provide a yielding under the required vacuum influences topermit the stencil and surface being decorated to come into intimatecontact.

It should also be noted that by compartmentalizing the ink housing 11,different colored inks may be employed simultaneously rendering amulti-colored image.

It will be understood that various changes in the details, materials,setups and arrangements of parts, which have been herein described andillustrated in order to explain the nature of the invention, may be madeby those skilled in the art Within the principle and scope of theinvention as expressed in the appended claims.

I claim:

1. An apparatus for stencil printing comprising in comhination:

(a) means mounting a stencil member in operative position;

(b) a flexible sealing member attached to said means, having a dependingportion surrounding the stencil member around its periphery in spacedrelation thereto forming a recess thercaround; and

(c) a vacuum source communicating with the aforementioned recess througha port means in the sealing member.

2. The apparatus of claim 1 wherein the depending portion of theflexible sealing member is in non-coplanar relation to the plane of thestencil.

3. The apparatus of claim 2 wherein the aforesaid means mounting astencil member in operative position comprises as a unitary componenttherewith an ink package containing at least one color of ink.

4. The apparatus of claim 3 wherein said ink-package comprises:

(a) a walled chamber; and

(b) movable means coacting with said walled chamber for transmittingpressure to an ink carried therewithin.

5. The apparatus of claim 1 further comprising: a collapsibleink-package connected to said means mounting a stencil.

6. An improved stencil printing apparatus comprising:

(a) a housing member for enclosing a quantity of viscous fluid;

(b) a continuous flexible wall carried at one end of said housingmember;

(c) a stencil member recessed within the periphery of said continuouswall and supported by the housing member, said wall adapted for sealingengagement with a surface to be printed whereby to form a chamberbetween the stencil and surface;

(d) piston means coacting with said housing member for transmittingpressure to a viscous fluid carried therewithin; and

(e) means for Withdrawing atmosphere from the aforesaid chamber causingthe flexible wall to yield, thereby permitting the stencii and surfaceto be decorated to come into intimate contact with one another.

References Cited UNITED STATES PATENTS 2,239,619 4/1941 Murgatroyd etal. 101-126 X 2,966,116 12/1960 Harris et al 101-405 X 3,172,358 3/1965Weiss 1()1115 X ROBERT E. PULFREY, Primary Examiner.

F. A. WINANS, Assistant Examiner.

